Web tensioning method and apparatus



June 4, 1968 P. NASH WEB TENSIONING METHOD AND APPARATUS 2 Sheets-Sheet 1 Filed Jan. 17, 1966 June 4, 1968 P. NASH WEB TENSIONING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Jan. 17. 1966 United States Patent assaess was TENSXGNlNG Marriott AND ArrAnA'rUs Paul Nash, 1071 Balrervale Drive,

Ottawa, Ontario, Canada Filed llan. 17, 1%6, Ser. No. 523L291 Claims priority, application Canada, Jan. 22, 1965, 921,436 6 Claims. (Cl. 226-1) ABSTRACT OF THE DISCLUSURE A method and apparatus for applying tension to a moving web of sheet material such as paper so as to remove web flutter without damaging the web, and in which an elongated, movable shoe having an uninterrupted, smooth and flexible web contacting surface is held in contact with the moving web by fluid at a pressure suflicient to remove flutter, the fluid being contained in a pressure liner. There being available if required means to automatically regulate the fluid pressure in response to a web flutter detector.

This invention relates to a web tensioning method and apparatus and in particular to a web tensioning method and an adjustable, flexible camber, web tensioning apparatus which is particularly adapted for tensioning wide, moving webs of sheet material such as paper for the purpose of substantially removing web flutter no matter where such flutter occurs across the length of the moving web.

More particularly this invention will be found to be capable of eliminating a loose edge on wide webs of moving sheet material so that a section of said material unsupported between two spaced parallel rollers flows in a steady plane without any part of the unsupported web exhibiting flutter or whip. Also such a result can be achieved without in any way damaging even fine surfaced sheet material such as paper.

During the manufacture of sheet material such as paper the usual practice is to form the material as a continuous web which may have various widths and subsequently treat this web to impart the desired characteristics to the material. After treatment, the finished web must often be inspected for flaws of various types before being packaged or wound in rolls for shipment.

It is well known that in the forming and subsequent treatment of webs of sheet material such as paper it frequently happens that after finishing but before inspection and/ or winding in rolls the tension of the web across its length varies to a substantial extent with, for example, the centre portions being quite tight and the marginal portions quite loose. This is particularly noticeable in very wide webs and in those webs which during some stage in their finishing have been passed over a Mount Hope roller, that is a roller whose axis of rotation is curved. As a result of this unevenness in tension across the web, portions of it will tend to flutter between rollers in the finishing and inspecting apparatus and in certain forms of sheet material inspecting apparatus this flutter is a disadvantage in that occasionally it will lead to erroneous indications of the presence of faults in the web being inspected. Also the resultant uneven tension makes it difiicult to wind the web up properly. In particular one edge of the material only may exhibit looseness and flutter and such can often not be tolerated.

Consequently when a web of sheet material which is to be inspected for faults is passed unsupported between two rollers through the sheet material inspecting appa- Patented June 4;, 1968 ratus, it is preferable that the tension of the web across its length be made fairly constant within certain tolerances acceptable to the inspection apparatus so that the web stays in a constant plane during inspection.

Accordingly there is a need for a suitable form of simple and reliable web tensioning apparatus which will place the web under sufficient tension to remove, or reduce to an acceptable extent, flutter in the sheet material caused by unequal tension in the web across its length. Of course such apparatus must not in use damage in any way the continually moving web whose tension it is controlling.

It is known to tension moving webs of sheet material by passing such a web over a pair of spaced parallel rollers between which is located apparatus including a partially enclosed air chamber and an air blower whereby air under low pressure may be applied to the moving web across its length. However, one disadvantage of this known web tensioning apparatus is that the pressure across the length of the web cannot be adequately controlled in that the sides of the air chamber must be spaced somewhat from the edges of the moving web of material. Such a spacing permits the escape of air at the edges of the web thereby causing a substantial pressure loss at the edges and thus prevents the reliable control of web edge fiutter due to looseness in the edge of the web. Of course with a wide web there is some tendency for it to move to one side or the other on the rollers when running and for this reason the side plates of the air chamber must be spaced a sutficient and normally greater distance from the edges of the web of material being run to insure that the web is not damaged. Such spacing will aggravate one of the main disadvantages of this prior art apparatus by making it even more difficult to maintain adequate air pressure on the marginal edges of the web and thus to control edge flutter.

Also it will be appreciated that in this known apparatus a substantial volume of air will be required because of losses. Therefore large blowers will have to be employed and of course such are incapable of developing very high pressures and under some circumstances will not be able to develop the pressure required to remove looseness to an extent adequate to remove flutter even other than at the edges of the web.

It is also known to control the tension in a moving web of sheet material by pinching the sheet material be tween a fixed bar and a plurality of independent semicircular shoes resiliently biased towards the fixed bar by means of an air inflatable liner. It is possible to control this pinch effect by adjusting the air pressure in the liner. However, for a number of reasons, such a form of apparatus cannot be utilized on many forms of sheet material such as fine papers of the type which it is required to inspect by the apparatus mentioned above. Firstly the pinch effect and resultant friction will frequently damage paper passing through this apparatus to an extent suflicient to render the paper unacceptable to customers. Tearing will also result, leading to down time for the web conveying apparatus while it is rethreaded. Also a further disadvantage of the known apparatus resides in the use of a plurality of shoes which will also damage the sheet material and particularly its surface, if it is a fine surface, by reason of the interrupted web contacting surface provided by such shoes. Such an arrangement can thus not be tolerated. In fact it would appear to be almost impossible to control web edge flutter, in an unsupported web section, with this known apparatus which is designed to avoid a break in a web which contains hard lumps.

It is accordingly an object of the present invention to provide a method and apparatus for tensioning webs and particularly wide webs, so that the tension on such a web will be substantially evened out across the length of the Web to at least reduce to an acceptable extent, or eliminate flutter, as well as other problems resulting from transverse tension variances, which problems have been found to affect, in an undesirable manner, inspection apparatus such as discussed above.

A particularly important object of the present invention is to provide a method and apparatus capable of eliminating a loose edge in a fast moving web of sheet material so that a section of the web unsupported between two rollers will flow in a steady plane without any part of the unsupported web exhibiting flutter or whip, particularly at the edges.

There is therefore provided, in accordance with a broad aspect of this invention, a method for substantially evently tensioning a moving Web of sheet material across its entire width to remove web flutter comprising placing an elongated shoe having an uninterrupted, smooth and flexible web contacting surface in contact with said web so as to extend across the length of said web beyond one of its edges to beyond the other of its edges, applying pressure to said shoe so that the surface in contact with said web exerts pressure on said web and maintains suflicient fluid pressure on said shoe to substantially eliminate flutter in an unsupported section of said web entirely across its length.

There is also provided an adjustable, flexible camber moving web tensioning apparatus which includes a suppirting structure, a shoe provided with an uninterrupted, smooth and flexible web contacting surface, shoe mounting means securing said shoe to said structure so as to permit movement of said shoe towards and away from a moving web with which said surface is in contact, and means co-operable with said structure and said shoe for exerting a variable pressure on said shoe in a manner such that said web contacting surface will exert pressure on a web with which said surface is in contact to tension and remove local looseness in said web thereby to remove local flutter.

In the accompanying drawings which illustrate preferred embodiments of this invention particularly adapted for use in combination with a known type if sheet material inspection apparatus;

FIGURE 1 is a schematic, end view showing one way in which the web tensioning apparatus of this invention can be employed with a known form of sheet material inspection apparatus;

FIGURE 2 is a detailed side view of the Web tensioning apparatus of FIGURE 1 with some parts broken away;

FIGURE 3 is an end view of the apparatus if FIG- URE 2;

FIGURE 4 is a section taken along the line 4-4 of FIGURE 2;

FIGURE 5 is a perspective view of a portion of a shoe used in the web tensioning apparatus of FIGURE 2;

FIGURE 6 is a perspective view of a portion of an alternative form of shoe for the web tensioning apparatus of FIGURE 2, this figure being found on the first sheet of drawings; and

FIGURE 7 is an end view of the apparatus of FIG- URE 2 using the shoe of FIGURE 6, this figure also being located on the first sheet of drawings.

With reference to FIGURE 1, the web tensioning apparatus generally referred to by the reference numeral 1 is shown located between a pair of spaced rollers 6 and 7 and in contact with a web 3 of sheet material moving in the direction of arrow 4, under roller 6, over roller 7, which rollers are located ahead of the sheet material inspection apparatus generally referred to by the reference numerals 9, 9 and fully disclosed in Canadian Patents Nos. 608,103 issued Nov. 8, 1960, 636,717 issued Feb. 20, 1962, 636,813 issued Feb. 20, 1962, 637,535 issued Mar. 6, 1962, and 638,763 issued Mar. 27, 1962 and corresponding to United States Patents 3,105,151 and 3,105,- 152 issued on Sept. 24, 1963, (all to Paul Nash). After i: passing through the inspection apparatus 9 the web 3 passes over roller 10, under roller 11 and then normally onto a winder.

Any suitable control means 8 may be utilized responsive to the detection means, for the purpose of actuating the control means 1, e.g., by connecting it to a source of fluid under pressure.

Usually the web tensioning apparatus 1 will be mounted in the framework (not shown) of the sheet material inspecting apparatus so as to be manually adjustable at least in a direction substantially perpendicular to the path of travel of the web 3, if not also in other directions. Such an adjustable mounting can take any desired form depending upon the particular form of apparatus on which the web tensioning apparatus is to be mounted.

Referring now to FIGURES 2 to 5 inclusive, the web tensioning apparatus 1 includes a supporting structure in the form of an elongated, open-bottomed, channelshaped housing 15 provided with three fitted, transverselyextending separator plates 16 which are secured to the housing 15 by means of screws 17. Separator plates 16 in conjunction with a pair of identically-shaped end plates 18 divide the housing 15 into four open-bottomed chambers 19 of substantially equal length. End plates 18 are secured to the respective ends of housing 15 by means of screws 20.

An opposed pair of retaining strips 22 are secured by screws 23- along the entire length of the housing 15 at its inside bottom edges as clearly shown in FIGURE 3.

Located within each of the chambers 19 is a pressure liner 25 which is inflatable to and maintainable at any desired pressure by means of conduit 26, in this embodiment an automotive type tire valve housing from which the valve has been removed. Conduit 26 passes through, and is secured to, the upper wall of housing 15 by a nut 27 in a conventional manner. The pressure liner may be suitably formed from sections of an inner tube.

Referring now in particular to FIGURES 2 and 4, it will be seen that there is also located in each of the chambers 19 a U-shaped inner shoe 30 whose length is only slightly less than the length of the chamber 19 Within which it is located. Normally the inner shoe 30 will be formed of a sheet material such as nylon which is flexible and is also capable of moving against those portions of the apparatus with which it comes in contact during operation of the apparatus, with a minimum amount of friction. This shoe is provided primarily to reduce friction of various parts of the apparatus on the liners 25, which friction if severe might cause premature failure of the liiters 25 thereby causing the tensioning apparatus to fai.

Referring now in particular to FIGURE 5, there is shown one form of flexible camber, outer shoe 31 which constitutes a part of the web tensioning apparatus 1. The outer shoe 31 is formed from a length of suitable sheet material and is provided with upturned side edges 32 which, to permit flexing of the shoe 31, are notched along substantially their entire length to provide a plurality of equally-spaced, inverted key-hole shaped notches 33 between which are located tongues 34. The free ends of each of the tongues 34 are turned outwardly to provide lips 35 which as shown in FIGURES 3 and 4 engage with the retaining strips 22 to limit outward movement of the shoe 31 when the shoe is installed in the housing 15. Installation is accomplished by inserting the shoe 31 into the housing from one end so as to be positioned as clearly shown in FIGURES 2 and 3.

Each of the ends of the upwardly turned side edges 32 are left free of notches and when the shoe is installed in the housing these ends project beyond the respective end plates 18 of housing 15. Shoe 31 is prevented from sliding out of position by means of a pair of retaining clips 38 which are clipped one to either end of the outer shoe 31 as clearly shown in FIGURE 3. Retaining clips 38 it will normally be formed of a resilient material such as thin spring steel.

As the outer shoe 31 must be capable of readily flexing and be resistant to the wear caused by the sheet material passing over it, certain types of sheet material have been found preferable for use in forming it, such as for example of Phosphor bronze material having a thickness of approximately of an inch. Other suitable sheet material from which the shoe can be formed includes beryllium, copper, steel or any other generally flexible and strong spring material.

As an alternative or addition to the shoe 31 illustrated in FIGURE 5, the shoe 41 as illustrated in FIGURE 6 may be employed. As will be seen from FIGURE 6, the modified shoe 41 may be, as with the shoe 31, provided with notches 33 and tongues 34 but these are located only along one upturned side edge 32 of the shoe. The shoe 41 extends from that edge provided with the notches 33 and tongues 34 in a gradual curve so as to be more or less semi-circular in cross-section as clearly shown, and the side opposite side edge 32 is apertured along its length at 42 to permit it to be secured to the housing as shown in FIGURE 7. The side edge 32 engages with a retaining strip 22 in the same manner as does the shoe 31. In this arrangement the sheet material would travel over the shoe from left to right as viewed in FIGURE 7. This particular shoe construction makes it necessary to have only a single retaining strip 22 and no retaining clips 38 are required, a fact which permits the shoe 41 to be made the same length as the housing 15. Also modified shoe 41 is easily replaceable when necessary as a result of it being exposed to wear due to friction against the fast moving sheet material. When shoe 41 is used in addition to shoe 31, shoe 41 may be in its simplest form a flat, thin metal sheet (steel-shim stock of an inch thick for example), secured to shoe 31 by flexible strips of plastic or rubber, or spring clips attached only to the non-web-contacting side of shoe 41 facing the U-shaped housing.

The main purpose of utilizing an overlying, protective shoe 41 in this manner is to avoid wear on the main shoe 31 which is more expensive to manufacture. Also use of an overlying shoe 41 makes it possible to manufacture shoe 31 in sections rather than in one continuous length thus often resulting in a further saving as the longer the length of shoe 31, often the greater will be the expense involved in its fabrication, as compared with a number of shorter shoes.

It will be appreciated that with either of the shoe arrangements disclosed the shoes 31 or 41 will be movable to a limited extent, towards and away from the bottom opening in the housing 15. The maximum outward extent of this movement for shoe 31 is shown by dotted lines 45 in FIGURE 3 wherein the shoe 31 is shown in its normal operating position. In other words shoes 31 and/or 41, are free to a limited extent to float with respect to the opening in the bottom of housing 15.

In using the web tensioning apparatus of this invention, the apparatus is mounted as schematically illustrated in FIGURE 1 with the shoe, whether it be shoe 31 and/or shoe 41, substantially as positioned in FIGURE 3. The shoe in contact with the web should extend across the web and beyond its edges. Compressed air is then fed into each of the liners 25 by way of its respective conduit 26 with sufficient pressure being applied to reduce web flutter to an acceptable level without damaging the web. If for example the tension in the marginal portions of the web passing under roller 6 is less than that in the centre portions of the web, then the end liners 25 will require a slightly greater air pressure than the centre liners 25. Once suitable operating pressures for the liners have been provided for any particular web, the web tensioning apparatus will normally continue to function in the required manner, that is to even out and provide the proper tension across the length of the web without further attention 6 as the flexibility of the shoe 31 and/or 41 combined with that of the inner shoe 30 and the resiliency of the inflated liners 25 will tend to automatically compensate for any small variances in web tension. Thus the web when passing under the sheet material inspection apparatus 9 will either be entirely free of flutter or will flutter only to an acceptable extent.

The web tensioning apparatus of this invention could be modified by removing the separator plates 16 and replacing the four liners disclosed in FIGURES 1 to 5 with a single liner having a single conduit. The four inner shoes 30 could also be replaced by a single, long inner shoe slit for flexibility. Inflation of such a liner to a suitable pressure will be found to even. out variances in web slackness across its length and even at its edges in quite an acceptable manner.

Also variable pressure may be applied to the shoes 31 and/or 41 by other than liners 25. For example mechanically adjustable, foam rubber or plastic pads backed by metal or other solid material could replace the liners, the pads being movable mechanically and also as a result of their resiliency to provide suitable pressure on the shoes.

Furthermore as certain types of sheet material inspection apparatus are in themselves capable of detecting flutter it is quite practical for such apparatus to be modified to automatically vary the pressure in the web tensioning apparatus liners 25 or pads to compensate for any flutter which might result through a change in web tension While being inspected. Thus it is possible to automatically maintain any desired uniform web tension along the entire width of the web without manual adjustment of the air pressure in the liner. For example the signal intelligence proportional to web flutter generated in sections of the inspection head (as disclosed in some of the previously mentioned Canadian and United States patents) corresponding to sections of the flexible camber web tensioning apparatus can operate for each camber bar section a three-way valve by an electro-mechanical transducer (several forms of which are well known in the art) so that the liner 25 or the pad is set to eliminate the web flutter. Such a three-way air valve conveniently has one inlet connected to a source of pressure, a second inlet to liner 25, with its third inlet being open to atmosphere.

Clearly various other arrangements can also be used to automatically convert the signal intelligence received from the inspection apparatus to mechanical movement to adjust pressure in the liners 25 or on the pads or any other suitable pressure applying means.

In summary, the present invention provides a simple and yet reliable, flexible camber web tensioning apparatus which is particularly suitable for use in controlling the tension of webs being inspected for faults but which is also useful for controlling and adjusting web tension for other reasons such as to insure proper winding of a web on calenders, winders, paper machines, etc., such as used in a paper-making plant.

I claim:

1. A method for substantially evenly tensioning a moving web of sheet material across its entire width to remove web flutter comprising placing an elongated shoe having an uninterupted, smooth and flexible web contacting surface in contact with said web so as to extend across the length of said web from beyond one of its edges to beyond the other of its edges, applying fluid pressure to said shoe so that the surface in contact with said web exerts pressure on said web and maintains sufficient fluid pressure on said shoe to substantially eliminate flutter in an unsupported section of said Web entirely across its length.

2. The method of claim 1 further including the steps of detecting the presence of unwanted flutter in said unsupported section and controlling said. applied pressure automatically by means responsive to a signal from said flutter detecting means.

3. An adjustable, flexible camber moving web tensioning apparatus comprising a supporting structure, a shoe provided with an uninterrupted, smooth and flexible web contacting surface, shoe mounting means securing said shoe to said structure so as to permit movement of said shoe towards and away from a moving web with which said surface is in contact, and means co-operable with said structure and said shoe for exerting a variable pressure on said shoe in a manner such that said web contacting surface will exert pressure on a web with which said surface is in contact to tension and remove local looseness in said web thereby to remove local flutter.

4. The apparatus of claim 3 wherein said variable pressure exerting means constitutes a fluid inflatable liner located within said supporting structure.

5. The apparatus of claim 4 wherein said supporting structure consists of an elongated housing provided with an opening in one side, said opening being covered by said shoe and said liner being located within said housing.

6. An adjustable flexible camber apparatus for tensioning unsupported sections of moving webs comprising;

(1) an elongated open sided housing of substantially U-shaped cross-section and having closed ends,

(a) a pair of shoe retaining strips secured to said housing, one being located on each of the inside longitudinal extending edges of the opening,

(2) a fluid inflatable liner located within said housing,

(3) and an elongated shoe provided with an uninterrupted,

smooth and flexible web contacting surface overlying said opening in said housing,

(A) each of the longitudinal edges of said shoe being upturned and notched at closely spaced intervals along their length,

(a) the free edge of each of said edges being turned outwardly so as to lie substantially in a plane parallel with said Web contacting surface;

said free edges being engageable with respective shoe retaining strips to secure said shoe to said housing while permitting limited movement of said shoe towards and away from said housing.

References Cited UNITED STATES PATENTS 3,111,285 11/1963 Coker et al 242--75.2

FOREIGN PATENTS 235,602 1/1964 Austria. 369,090 5/ 1963 Switzerland.

ALLEN N. KNOWLES. Primary Examiner. 

